I always leave mine forward. To me (idk if this is correct or not) I think having the valve spring compressed is ok because the pressure from the gas will help seal it anyway. All the valve spring is used for is to push back the valve pin and cup seal after the hammer has hit it. So if the valve spring is not as stiff as it used to be it's ok, it's just going to be a little more inefficient and blow more air through the valve to re-cock your marker than it needs to.